It is true that democracy can indeed be slow to respond to a crisis, but look how fast the US government moved in the wake of the 9-11 attacks. Whether you liked or disliked those post-attack outcomes, you had to admire how spry all the actors suddenly became when there was truly a crisis.
I believe that many people simply don't think there is a big environmental crisis. Global warming, sinking islands and melthing glaciers do not (yet, anyway) seem to have moved people quite the same way that burning rivers or smog once did. One of the most discouraging things for me was the recognition that the two major candidates barely discussed these concerns in their televised debates.
My goodness, I would have loved for them to say what their concerns were for global warming, never mind what happened at Fukushima. Never mind the several other major troubling environmental trends (deforestation, depletion of the seas, over-population, etc) that barely get a blip beyond forums like this one!
I think democracy can work well in a crisis, when there is a sense of common purpose. Will we ever reach that point?